CLASS I ANTHOZOA 69 
pair of mesenteries, the infolded ectoderm secretes small, round, oval, or irregular 
caleareous bodies (sclerites); these are opposed against one another in radial 
directions, and as others are successively laid down on the top of them, upright 
partitions or septa (Sternleisten, cloisons) are built up. Gradually, also, as the 
polyp approaches maturity, the basal plate becomes calcified, owing to the 
secretion by the outer surface of the ectoderm of numerous minute, closely 
erowded, caleareous bodies. The septa, however, grow considerably above the 
base, and become lodged in the vertical interspaces between the mesenteries. 
In the same manner, within the soft. body-wall, a calcareous secretion may 
take place, binding the outer edges of the septa together, and known as the 
wall or theca (Mauer, Wand, muraille). Both septa and theca are composed ot 
minute, densely crowded caleareous bodies, in which delicate caleareous fibres 
may be seen radiating in all directions from a central dark space. And _ since 
THe 
i> 
GA 

























Fic. 101. 
Fic. 100. Astroides calycularis, Lamx. sp. Mediterranean 
(after Lacaze- Duthiers). Enlarged longitudinal 
Corallium rubrum, Lam. (after Lacaze-Duthiers). section of polyp with calcareous skeleton. te, Ten- 
Branch of red coral of commerce laid open along tacles ; 0c, Oesophagus ; me, Mesentery ; loc, Mesen- 
the axis, and showing three polyps in section em- terial pouches; coe, Coenosark; spt, Septum ; 
bedded in fleshy coenosark. col, Columella. 
all the calcareous bodies forming the septa have a radial disposition, the 
calcification-centres as seen in transverse sections form a dark, mostly inter- 
rupted, and occasionally jagged median line, from which bundles of minute 
fibres radiate outward in all directions. Similar ealcifieation-centres are found 
also in the theca. Sometimes the median dark line is uninterrupted and 
divides the septum into two separate lamellae. 
The interstices between the sclerites forming the septa are either completely 
filled with carbonate of lime (Aporosa), or there remain larger or smaller porous 
spaces (Perforata) ; in many cases, in fact, the septa are represented by a loose 
network of sclerites piled up vertically, or merely by vertically directed spines. 
The number of mesenteries and septa within the visceral chamber is equal 
to that of the tentacles, and is somewhat uniform throughout the different 
sub-classes, orders, genera, and species. Increase takes place, as a rule, in such 
a manner that whenever, as the polyp grows, a new visceral chamber is formed, 
5) eats 
“< ASA 1A / or 
= SDL oA 
